Annals of Glaciology 53(60) 2012 doi: 10.3189/2012AoG60A152 147 Glaciar Jorge Montt (Chilean Patagonia) dynamics derived from photos obtained by fixed cameras and satellite image feature tracking Andre´s RIVERA,1,2 Javier CORRIPIO,3 Claudio BRAVO,1 Sebastia´n CISTERNAS1 1Centro de Estudios Cientı´ficos (CECS), Valdivia, Chile E-mail: [email protected] 2Departamento de Geografı´a, Universidad de Chile, Santiago, Chile 3meteoexploration.com ABSTRACT. Tidewater calving glaciers can undergo large fluctuations not necessarily in direct response to climate, but rather owing to complex ice–water interactions at the glacier termini. One example of this process in Chilean Patagonia is Glaciar Jorge Montt, where two cameras were installed in February 2010, collecting up to four glacier photographs per day, until they were recovered on 22 January 2011. Ice velocities were derived from feature tracking of the geo-referenced photos, yielding a mean value of 13 Æ 4md–1 for the whole lower part of the glacier. These velocities were compared to satellite- imagery-derived feature tracking obtained in February 2010, resulting in similar values. During the operational period of the cameras, the glacier continued to retreat (1 km), experiencing one of the highest calving fluxes ever recorded in Patagonia (2.4 km3 a–1). Comparison with previous data also revealed ice acceleration in recent years. These very high velocities are clearly a response to enhanced glacier calving activity into a deep water fjord. 1. INTRODUCTION Warren and others, 1995; Rignot and others, 1996a,b). Another SPI glacier with direct ice velocity measurements is The Patagonian icefields have been shrinking at high rates in –1 the last 50 years, compared to the area losses experienced Glaciar Tyndall, where a maximum of 1.9 m d was meas- since the Little Ice Age, contributing significantly to sea- ured in 1985 near the medial moraine (Kadota and others, level rise (Glasser and others, 2011). The Southern Patagonia 1992). Most of these ice velocities were obtained by Icefield (SPI; Campo de Hielo Sur), in the Southern Andes of measuring stakes, seracs, erratic blocks or other features on Chile and Argentina, is the largest temperate ice field in the top of the glacier, by theodolite. More recently, satellite Southern Hemisphere, with 48 main basins and nearly images (Floricioiu and others, 2009) and continuous GPS 13 000 km2 of ice (Aniya and others, 1996). Most of its measurements (Sugiyama and others, 2011) have been used. glaciers are calving into lakes or fjords, with the majority of Terrestrial oblique photography has been applied to at least them, including Glaciar Jorge Montt, experiencing strong one glacier in Patagonia (Hashimoto and others, 2009, 2011). frontal retreat and thinning at very high rates during recent The first published velocities from Glaciar Jorge Montt were from Enomoto and Abe (1983) who measured years (Aniya and others, 1997; Rignot and others, 2003). –1 Among the few exceptions are Glaciar Moreno which is 240 m a at a western non-calving tongue. Using speckle stable and Glaciar Pı´o XI which has advanced (Masiokas and tracking from RADARSAT-1 images collected in September– November 2004, E. Rignot (personal communication, 2011) others, 2009). –1 Glaciar Jorge Montt (488190 S, 738290 W; ice basin area obtained values of 9–10 m d 3 km upstream of the glacier 500 km2 in 2011) is one of the main tidewater calving front. In this paper, these values are compared to ice glaciers of the SPI. It flows north from the local ice divide velocities derived from fixed cameras installed near the (1600 m a.s.l.) located within one of the main plateaus of glacier edge, pointing toward the lower tongue of Glaciar the SPI, to calve into an unnamed fjord that opened as a result Jorge Montt and operating almost continuously between of the glacier retreat experienced since 1898 (Steffen, 1910), 9 February 2010 and 15 January 2011. These results are also yielding a total retreat of 19.5 km until 2011 (Fig. 1). Very compared to feature-tracking ice velocities derived from little is known about how glacier velocities are reacting to Advanced Spaceborne Thermal Emission and Reflection these significant changes. Very few ice velocities have been Radiometer (ASTER) images collected in February 2010. measured in the SPI, resulting in a wide rate range, from a few meters per day at Glaciar Moreno with some seasonality (Stuefer and others, 2007; Ciappa and others, 2010; 2. INSTRUMENTS, DATA AND METHODS Sugiyama and others, 2011), to a mean ice velocity near In January 2010, a field campaign was conducted to Glaciar the front of Glaciar Pı´o XI of 20 m d–1, with maximum values Jorge Montt, the main aims of which were to study the of 50 m d–1, when surging behaviour was suggested (Rivera sedimentation rates near the glacier front, the long-term and others, 1997). One of the glaciers with more direct ice glacier variations, the oceanographic conditions at the new velocity measurements is Glaciar San Rafael, Northern fjord opened by the glacier retreat and the ice velocities. Patagonia Icefield (NPI; Campo de Hielo Norte), where up This last topic of research is the main focus of this paper. to 17–20 m d–1 was detected near the tidewater calving During the field visit, many icebergs and brash ice glacier front (Naruse, 1985, 1987; Kondo and Yamada, 1988; blocked most of the fjord, making it difficult to survey the 148 Rivera and others: Glaciar Jorge Montt dynamics Fig. 1. Jorge Montt glacier frontal variations, 1945–2011. C1 and C2 are the locations of the fixed CANON cameras discussed in the text. The background is an ASTER image from 2008. The red box A indicates the area with ice velocities described in Figure 5. The green box B is the area with ice velocities described in Figure 6. The black line C is the location of the profile used for comparison purposes in Figure 7. inner fjord. Despite these difficulties, a metal boat landed ensure the cameras’ operability until the data were near the glacier front at its western margin allowed the recovered a year later. These cards were designed to glacier margin and other local features to be measured using regulate the voltage and activate the camera up to four JAVAD model Lexon GD dual-frequency GPS receivers. Two times a day. They were made by two d.c–d.c. converter spots located 198 m apart were considered suitable for modules in cascade. installing the photographic cameras, because they gave Camera C1, using a focal length of 25 mm, successfully privileged views of the lower tongue of the glacier. These operated between 8 February and 30 October 2010, spots were drilled and a metal pin point was glued to the collecting four photos per day at 08:00, 12:00, 16:00 and rock hole. The GPS receivers were installed on top of this 20:00 local time. Camera C2, using a focal length of 18 mm, metal pin for 30 min to give a position of 20 cm accuracy operated continuously between 8 February 2010 and after PPS (Post Processing Software) post-processing (C1 and 15 January 2011, collecting four photos per day. Cameras C2 in Fig. 1). Two metal boxes were installed and tied to the were triggered by an external timer and could not be above-described metal points, in order to site the cameras synchronized. (Fig. 2). Plastic suitcases containing the cameras were installed in the metal boxes. Two digital CANON EOS Rebel xti 400D 10.1-megapixel 3. GLACIER SURFACE VELOCITIES FROM cameras were used in the field, featuring a complementary TERRESTRIAL CAMERAS metal oxide semiconductor (CMOS) sensor of 22.2 mm  14.8 mm with an aspect ratio of 3 : 2 (horizontal/vertical), 3.1. Camera orientation including EF-S lenses with focal distances of 18–55 mm and Only two well-measured ground-control points (GCPs) a maximum aperture of 1 : 3.5–5.6. The internal batteries of are visible from each camera, and at least three points are the cameras were supplemented by 12 V 40 Ah batteries needed for space resection or exterior orientation of the connected to electronic cards including a timer, able to image (Luhmann and others, 2006). In order to obtain the Rivera and others: Glaciar Jorge Montt dynamics 149 camera orientation with the available information, we used a DEM (digital elevation model, ASTERGDEM, 30 m reso- lution) and a procedure developed by Corripio (2004) for geo-referencing oblique images. This procedure establishes a mapping function between image space and object space by projecting the processed DEM to oblique image and adjusting camera attitudes for the best fit between two data in two-dimensional image space (Fig. 3). The procedure has been successfully applied to an ice-capped volcano in southern Chile (Rivera and others, 2008). Fine adjustments were made manually, by changing the viewing direction vector until the DEM matched the image, indicating that camera orientation was correct. This procedure identifies both the viewing direction and the roll of the camera, or rotation around the axis defined by the viewing direction b vector (N in the camera coordinate system). Once the orientation is known, the camera reference system is defined b b b by the orthogonal vectors U, V, N (Fig. 4). 3.2. Feature tracking from stereo pair Two cameras were installed overlapping large sections of Glaciar Jorge Montt near the snout at a hill with a good view of the lower part of the glacier (Fig. 1). By precisely identifying the lines of sight from each camera with the same points on the ice, on nearly simultaneous (<3 min apart) images from both cameras, the approximate location of these points could be inferred.